The present invention relates to an improved aeration apparatus for use in sewage treatment plants to dissolve oxygen into the sewage, and more particularly to an improved aeration apparatus for use in combination with a single home sewage treatment unit.
At the present time, most single-family homes and small multiple-family homes that are not connected to a central sewer system employ a septic tank system for the disposal of biodegradable wastes, particularly sewage. These tanks are generally of very low efficiency in processing these wastes, and, as a result, often tend to pollute the environment. Because of the well known pollution problems that are generated by septic tank systems, regulatory authorities in many areas have banned the use of such tanks, and it is expected that such bans will become more prevalent in the future. Accordingly, there is a need for a high-efficiency unit for the treatment of biodegradable wastes which is compact, inexpensive, and can be used to provide such treatment for single-family dwellings and small multiple-family dwellings.
Generally, such units provide a means for treating a liquor containing biodegradable wastes which comprises delivering the liquor to a quiescent settling zone, in which large particulates are permitted to settle to the bottom where they are subjected to digestion by anaerobic microorganisms. The liquor is delivered from the settling zone to an aeration zone, where it is aerated, and is then delivered downwardly through a column of submerged fixed media. The fixed media is composed of a multiplicity of elements which are freely and randomly stacked on one another to provide interstitial area between them. These elements have a high surface area to volume ratio, so that aerobic microorganisms can grow on their surface to treat biodegradable wastes contained in the liquor. As a result of their random stacking and high surface area, the elements promote homogeneous contact of the liquor with the fixed media. The liquor is received at the bottom of the fixed media and recirculated through the aeration zone and back through the fixed media in order to provide multiple passes through the media for thorough treatment. After such treatment, the effluent that has passed through the fixed media is withdrawn from the unit.
The present invention is directed to an improved direct drive mechanical aeration apparatus for supplying the aerobic microorganisms with the oxygen required for them to multiply rapidly and supply the aerobic bacteria required for the aerobic metabolism of the sewage organics. If sufficient oxygen is not supplied, the bacteria operate on an anaerobic metabolic pathway and produce poor treatment and obnoxious odors.
The use of direct drive mechanical aerators have been used in the sewage treatment field for many years. These aerators have generally been mounted upon floats; an example of such is disclosed in U.S. Pat. No. 3,572,658. Another type of heretofore used mechanical aerator which is not float mounted and utilizes a draft tube to draw liquid up into the propeller is disclosed in U.S. Pat. Nos. 2,186,371 and 2,346,366. The present invention is an improvement upon the latter type of mechanical aerators and is specifically designed for use in a single home sewage treatment unit.
It is a primary object of the present invention to provide an improved direct drive mechanical aerator for use in sewage treatment plants to dissolve oxygen into the sewage which is highly efficient and therefore consumes less horsepower to supply the same quantity of oxygen.
Another object is to provide a direct drive mechanical aerator specifically designed for use in combination with a single home sewage treatment unit which makes use of the aerator motor fan to force air into the unit so that a fresh supply of oxygen is present at all times.
A further object of the present invention is to provide a mechanical aerator which prevents clogging at the propeller.
An even further object is to provide a mechanical aerator which protects the motor bearings from the inherent water spray.
These and other objects are realized in accordance with the present invention by providing an aerator which includes a motor assembly extending through the sewage unit cover, having a downwardly extending shaft, which in turn is secured to and rotates a propeller. The propeller extends downward into a draft tube so as to pump the liquid to be aerated upward therethrough such that it is thrown against a deflector plate and sprayed out radially in all directions. The thin film of liquid leaving the edge of the deflector plate results in a high transfer efficiency of oxygen from the air located in the space between the sewage unit cover and the liquid surface. A slinger is positioned about the motor shaft below the deflector plate. The slinger being of slightly larger diameter than the shaft opening in the deflector plate acts as a pump to prevent liquid from passing up through the area between the motor shaft and the deflector plate. Additionally, any liquid which might pass up through that area is allowed to pass back through an open area provided between the deflector plate and the motor. In this manner the motor bearings are protected from the inherent liquid spray. Besides being the prime mover, the motor also maintains an air oxygen layer between the liquid surface and the sewage unit cover. The motor fan pulls fresh air into an aerator housing through an air vent in communication with the outside. The fresh air passes through the motor where it is heated and passes out of the aerator housing through openings therein into the area above liquid surface. A seal is provided between the motor and the aerator housing to insure that only fresh air is pulled through the motor by the motor fan. To avoid clogging there is provided enough clearance between the draft tube and the propeller. Additionally, the propeller is free to move in one direction or another if a large object comes through the draft tube.